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Now we know what killed Knut the celebrity polar bear

Scientists have finally solved the death of Knut, the famous polar bear who graced the cover of Vanity Fair and rubbed shoulders with Hollywood A-listers.

Knut, who was raised in captivity in Berlin Zoo after being abandoned by his mother, drowned in 2011 after suffering an epileptic fit triggered by an unknown cause. Tests on his brain tissue have revealed that the four-year-old polar bear died from "anti-NMDA receptor" encephalitis, caused by the bear's immune system attacking his own brain cells.

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Although it's the first time this type of autoimmune condition has been found in non-humans, researchers -- who published their findings in Scientific Reports -- believe that it's probably much more common in both wild and domesticated animals than widely thought.

Dr Harald Pruess, an expert in human brain disease and based at the German Center for Neurodegenerative Diseases, first recognised some similarities in Knut's post-mortem reports with human sufferers of the condition, after initial tests failed to pinpoint the cause of death.

He explained to reporters: "Antibodies that normally help to defend us against viruses or bacteria can obviously under certain circumstances turn against their own body and attack nerve cells. "In the most common autoimmune encephalitis, these antibodies bind to a glutamate receptor in the brain called NMDA receptor and cause seizures, cognitive impairment, psychosis or coma."

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Four-year-old Knut was perhaps the most recognisable polar bear on the planet, regularly featuring on TV and magazine covers, with the public seemingly fascinated by his tragic beginnings. Even his death was played out in the public glare, after he suffered the fatal fit in front of several hundred zoo visitors on 19 March 2011.

Now it's hoped that the publicity surrounding his death will help to raise awareness of anti-NMDA receptor encephalitis -- which affects around one in 200,000 people every year -- and help future diagnosis and treatment of both human and animal sufferers.